The demand for consumer goods such as mattresses, quilts, side parts of motor vehicles, room decorations, garments, mattress cover pads, diamond-quilted covering featherbeds, side and rear parts of easychairs, couches, couch seat covers, profiled backs of upholstered furniture, to mention only some, has suddenly increased so that the manual work must be eliminated which was previously required, e.g., to make quilted seams. The invention is based on the recognition that high-frequency seam welds are to be used instead of manually made quilted seams because high-frequency welding is an optimum method meeting the requirements which arise when fabrics of all kinds consisting of textile fibers and containing a filler or no filler must be profiled. In the high-frequency field, only the dipolar plastics material which is incorporated as a bonding material between the textile fabrics or webs to be joined by welding is heated to its melting point and subjected to pressure so that it begins to flow and will constitute the so-called seam weld having a very high strength whereas the sheets to be joined by welding are not subjected to an appreciable temperature rise so that the properties possessed by the unjoined sheets are not adversely affected, different from all other thermal bonding processes. A bonding material is required because a number of textile materials which are used can be welded only with difficulty. This applies, e.g., to foamed plastics materials, such as polyurethane foams, although polyurethane foams are of great importance as a filler for cushions, pads, linings of motor vehicle bodies, airplane cabins etc. so that dipolar plastics materials, particularly synthetic resins, must be provided between the so-called cold electrode or anode forming the so-called working plate and the hot counterelectrode, which has the configuration of the required seam weld, in order to ensure that the electron current flowing in the high-frequency field between the anode and cathode causes the dipoles contained in the dipolar plastics material to become aligned. The weldability of a plastics material in a high-frequency electric field depends on the welding factor, which is equal to the product of the dielectric constant, which is a measure of the insulation resistance of the dielectric, and the difference between .pi./2 and the tangent of the phase angle between current and voltage. The above-mentioned tangent of the last-mentioned angle delta depends on the alignment of said dipoles. If the product representing the welding factor is sufficiently high, the losses of electric energy will be converted into heat, which causes a melting of plastics materials, particularly synthetic resins, which are used as dipolar materials.
Hereinbefore, the physical processes have been stated which enable the use of high-frequency welding for joining virtually all textile fabrics in question by high-frequency seam welds so as to form composite webs or composite bodies and particularly to impart a profile thereto. Other requirements to be met arise because consecutively arranged machines, cyclic and production line processes are required for the sake of economy. As a result, only relatively short periods of time are available for joining the individual webs in a composite web. This requirement is also met by high-frequency welding in a particularly high degree because the electric energy loss which is converted into heat can be selected as required without difficulty. Additional requirements arise because of the desire for a high quality of the product. For instance, the flexibility and grip of the starting textile fabrics must not be adversely affected. More particularly, there must be no embritlement along the seam welds, regardless of whether these seams form dots, lines or strips. Another requirement is at least as important and resides in that the provision of such high-frequency seam welds must not alter the laundering and dry-cleaning properties of the products. For this reason, the bonding materials must resist detergents and dry-cleaning agents. Another requirement, which is just as important, resides in that the products must be permeable to gas (air) and liquid (moisture, vapor, sweat) so that garments made from such products will not distract from the comfort of the wearers thereof. The last-mentioned processing involves another requirement, which resides in that the bonding substances must be selected so that the layers in question may be joined by the processor himself so that this joining need not be effected where the material is made. For instance, if a manufacturer of garments desires to make a man's jacket having a predetermined, fitting shape, which should be durable, the product which supports the jacket fabric and imparts shape to it and holds it in shape must be adapted to be cut in the garment factory so that a conventional ironing operation is sufficient to stiffen and reinforce the outer fabric as may be desired. The above remarks do not fully define the requirements to be met and the technical objects based thereon. The listing is to be concluded by a reference to a particularly important requirement, which resides in that the required economy must be ensured in spite of the fact that the product is of optimum quality. It will be outlined below that this requirement can also be met by the invention.
Based on known materials which can be high frequency-welded, all objects mentioned above are accomplished according to the invention in that the material comprises a support, which is rustleproof and permeable to air and moisture and which carries particles of synthetic thermoplastic resins, such as polyamides, which resist washing and dry-cleaning and which are adapted to establish a bond under the action of high-frequency energy. As a result, the particles of synthetic resin may be provided on and fixed to the support in such a manner that they are discrete particles in the form of dust, powder, grains or agglomerates and assist the welding in dependence on the size and form of electrodes which are subjected to the high-frequency field. A number of advantageous possibilities reside in the arrangement of the particles in a geometrically ordered dot pattern. For instance, the particles may be arranged to form a preferably ordered line pattern, which may surround fields forming parallelograms having equal pairs of sides (rhombi).
It has already been pointed out that polyamides meet the requirements to be fulfilled as regards the resistance to detergents and dry-cleaning agents. Modified polyamides have the same property and additional properties, e.g., a high wear resistance. Modified polyamides are formed by a co-extrusion of a plurality of different types of homopolyamide granules to form so-called block copolyamides, which have melting temperatures and other properties lying in accordance with a virtually linear function between those of the homopolyamides forming these modified polyamides. The macromolecules comprise long blocks of the individual polymeric components; the length of these blocks depends on the degree of polymerization of the homopolyamides which are employed. Because the short residence time at elevated temperatures permits of only a slight conversion, these modified block copolyamides are in part only a physical blend of the components. True copolyamides of the type Nylon 6/6, 6/12 differ from the block copolyamides in that they exhibit a statistical distribution of the monomeric units in the macromolecule and are polyamides having modified properties. The crystallinity is reduced because hydrogen bridges cannot form to an appreciable extent. Depending on the composition in percent, the melting point is lowered and reaches a minimum in a eutectic mixture. Although such modified copolyamides are relatively expensive, their use within the scope of the present invention is still economical because surprisingly small amounts of the modified polyamide are sufficient to provide for the required bonding strength under the special conditions of high-frequency welding.
Copolyamides consisting of polycondensation products of hexamethylene diamine and adipic acid have proved particularly desirable. The same applies to products of epsilon-aminocarproic acid. Other suitable substances include polyamides of 7-aminoheptanic acid, 9-aminononanic acid, 10-aminodecanic acid, 11-aminoundecanic acid, as well as polyamides based on dodecalolactam or polylaurinlactam.
The bonding material may be provided on one or both of the boundary surfaces of the support. For instance, the bonding material provided on a boundary surface of the support may be enclosed between the latter and, e.g., a textile fabric or another layer which seals and covers the support, e.g., by sheeting which is made of various materials and which instead of a single covering layer may consist of a plurality of layers or a composite material. If the bonding material is provided on both boundary surfaces of the support, it will be inherent in this embodiment that the bonding material deposited on the support will be provided on each side of the support between the latter and a covering layer or set of layers.
The support may consist of a wide range of materials, preferably of foams, including polyurethane ester foams, non-woven fabrics, woven fabrics, bobinets, knitted fabrics, stitchable knitted fabrics, needle-punched pile fabrics, textile fabrics having adhered tufts, foam-bonded textile fabrics, cellulose, wadding and felt. The non-woven fabrics may have been formed by mechanical, aerodynamic and hydrodynamic methods as well as by spinning. Non-woven fabrics include also flexible bonded non-woven fabrics as well as bonded spun non-woven fabrics. These bonded non-woven fabrics may be mechanically or adhesively bonded, e.g. with or without a bonding agent, or they may consist of expanded or needle-punched non-woven fabrics. Reference should also be made in this connection to reinforced non-woven fabrics, which may be reinforced by arrays of filaments or threads, woven fabrics, knitted fabrics, nettings and plastics material sheeting.
Covering layers may be joined by calendering on one or both sides.
It has been mentioned hereinbefore that cellulose may be used as a material for the support carrying the particles of synthetic resin used as a bonding material. This is of great importance because it enables the support to be made from all thin sheets of felted fibers. Even a few fiber layers or only a single fiber layer will be sufficient for an adequate fixation of the minute amounts of particles of synthetic resin which are required in practice and for such a reliable support thereof that the support can be sold as such, particularly if it consists of wound-up fiber layers. The thickness of the support may be as large as or smaller than the largest dimension of a particle of synthetic resin provided on the support. The required economy will be particularly obtained if the fibers of the support consist of cellulose. The resulting support has a cellulose-like structure or consists of cellulose.
Thin sheets of foam are just as important. The support can perform the required functions even if it has a thickness of only 1.00-1.50 millimeters. The use of a smaller thickness is prevented only by the fact that the handling becomes difficult in practice. Such thin layers of plastics material may be produced by a peeling operation. The means which are available have been used to make sheets of foam which have the above-mentioned thickness of 1.00 millimeter and a smaller thickness throughout their area. This does not preclude the manufacture of even thinner foam layers by improved processes.
An upper limit is imposed by the requirement that the high-frequency welding must be uniform. The upper limit which has been numerically stated will vary with the high-frequency welding technology so that the figures stated are based only on the present state on the art in the fields concerned. The manufacture of a support having the small thickness stated without impairing the handling of the support, which must be considered a finishing material, can be performed in a simple manner if the foam consists of a polyurethane ester whereas, e.g., polyurethane ethers are less suitable or may even be unsuitable. Nevertheless, a tender and light-weight structure thus formed may be shipped well in the form of rolls and may be used in machines without danger of damage and may be handled in all other ways in question. It has been found, above all, that extremely favorable results may be obtained in the subsequent welding operation because a perfectly uniform distribution of the plastics material over the surface in question may be accomplished. The uniform distribution of the particles of bonding material throughout the surface of the finishing material results in perfectly uniform, homogeneous seam welds. If the particles of plastics material ar provided in a sufficiently dense distribution, these seam welds will no longer have a structure which can be recognized but will form the above-mentioned, continuous, homogeneous weld layer, which has a desirable durability and uniform response to the stresses applied. Particularly great advantages will be obtained because each particle of bonding material is used for welding whether it is directly subjected to the thermal influences during the welding on one boundary plane or on both boundary planes or between the two boundary planes of the support consisting of a thin sheet of foam. Although the particles of plastics materials which form dots or may have been rolled to form platelets or lenticles have a thickness which is virtually negligible relative to the other dimensions, such particle in the form of a dot, platelet or lenticle is entirely utilized for welding. As a result, an extremely small amount of plastics material per unit of welding area is sufficient so that the support on the one hand and the plastics material carried by the support on the other hand enable a very high economy to be achieved in the making and unwinding of the support and in the making of the plastics material carried by the support and in the operation of the machine used for these purposes.
Additional advantages are due to the fact that it is no longer necessary to use dispersions, which have virtually restricted the choice of plastics materials to PVA and/or PVC synthetic resins, which resist neither laundering nor dry-cleaning, although this is a great disadvantage. Besides, they can be dissolved by solvents, different from plastics materials which resist laundering and dry-cleaning and which can be applied directly without need to use a dispersion.
It is known to provide dressing materials consisting of individual layers joined by welding, preferably high-frequency welding, with bonding material inserts or facings in different main forms. To provide a so-called welding finish, non-woven fabrics have been sprayed with synthetic resins in the form of dispersions of synthetic resins consisting of polyvinylacetate and/or polyvinylchloride so that a marketable product was obtained when the dispersed particles of synthetic resin had been solidified. Composite materials required to have one or more layers of materials which have poor welding properties or which are adversely affected by a welding operation resulting in proper seam welds were made with the aid of machines for performing one or more needle punching operations so that the polyurethane foams, which were mainly used, were provided with an infinite number of stitch holes. The resulting fabrics enabled or improved the welding of the layers of dressing material in question. In a third process which has been used, those layers which cannot readily be welded to other materials were surface heat-treated at temperatures at which the boundary surfaces in question were at least tacky or even resulted resulted in the formation of a joint which can be described as a welded zone.
Papers, preferably in the form of tissue papers, which have been impregnated or coated with a solution of polyvinylchloride, have also been used in the high-frequency welding of foams. Tissue paper, however, is not a rustleproof support and lacks the essentially required permeability to air and water (moisture, sweat). An additional disadvantage resides in that the materials are highly embrittled along the welded zones. The feeding of strips and webs of paper involves a certain structural expenditure and a risk of a lateral displacement of the material to be welded relative to the bonding material. As a result, only straight-lined welded zones can be formed in this way whereas ornaments and curved welded zones cannot be obtained, unless the bonding material is adhered to one of the materials to be welded.
It is known to use bonding materials in powder form. In these processes, the synthetic resin powder is introduced directly into the zone of contract between the materials to be welded. As a result, joining processes must be carried out immediately after the manufacture of the materials to be welded whereas it has been possible according to the invention to provide a support which carries the particles of synthetic resin and which is available wherever the processing operations require a subsequent high-frequency welding, independently of the manufacture of the materials to be welded. This practice meets the above-mentioned requirement that the bonding material should be available whenever and wherever it is needed. The above-mentioned synthetic resin powders have been made only of polyvinylacetate (PVA), polyvinylchloride (PVC), polyvinylpropionate, polyvinylidenechloride, acrylic ester, and their copolymers. These plastics materials resist neither detergents nor dry-cleaning agents. The synthetic resins used in accordance with the invention and consisting of modified polyamides, e.g., those described as modified polyamides under the name Nylon 6/6, 6/12, resist detergents and dry-cleaning agents and have other desirable properties. Besides, the finishing materials and processes which have been disclosed before are not entirely satisfactory from the economic and/or technological aspects. The distribution of the particles of synthetic resin cannot be fully controlled unless the processes are employed which will be described hereinafter. The non-woven fabrics which have been used are relatively expensive and their cost cannot be adequately lowered even when they are made in large quantitites. Needle punching methods result in a considerable reduction of the strength of the needle-punched fabrics and/or layers becuase the penetration of the needles inevitably destroys or at least loosens the structure of the material at the penetration points. The surface heat-treating process may be carried out with success only by highly experienced, skilled persons which have had years of training and inevitably involves considerable dangers in operation.